To diversify programmable logic functions and promote their mounting in electronic devices and the like, a switch (switching device) which interconnects logic cells needs to be downsized to decrease the ON resistance. In this situation, switches using an electrochemical reaction are known to be smaller in dimension and lower in ON resistance than well-known semiconductor switches. A known example of the switching device using an electrochemical reaction is a two-terminal switch disclosed in reference 1 (Japanese Patent Laid-Open No. 2002-536840).
FIG. 12 shows the structure of a two-terminal switch described in reference 1. This two-terminal switch is configured by sandwiching an ion conducting layer 1203 between a first electrode 1201 and second electrode 1202 for supplying metal ions. Switching between the first electrode 1201 and the second electrode 1202 is done by forming and canceling a metal bridge in the ion conducting layer 1203. The two-terminal switch has a simple structure and a simple manufacturing process, and the device dimensions can be decreased to the nm order.
There is also proposed a three-terminal switch with three electrodes that has an ion conducting layer, similar to the two-terminal switch. By arranging the third electrode which controls formation and cancellation of a metal bridge, the three-terminal switch can control the thickness (range) of the metal bridge, improving electromigration resistance.
When the above-described device is applied to a logic device, a large current may flow through the two-terminal switch upon connection and disconnection to damage the logic device because the resistance of the metal bridge is low. The three-terminal switch can control the current because an electrode for controlling formation of a metal bridge and an electrode for transferring an electrical signal are arranged separately. However, the three-terminal switch is more complicated in structure than the two-terminal switch and the device dimensions tend to increase.
Mounting such a switch as the wiring switch of a programmable logic device requires a switching voltage (breakdown voltage) equal to or higher than the logic operating voltage and affinities for the CMOS (Complementary Metal Oxide Semiconductor) manufacturing process. The switching characteristic greatly depends on the material of the ion conductor, so selection and optimization of the ion conductor material are important. An ion conducting layer made of an oxide is promising because the switching voltage can be raised and an affinity for the CMOS manufacturing process is good. For example, reference 2 (Japanese Patent Laid-Open No. 2006-319028) discloses an example in which tantalum oxide is used as an oxide for the ion conducting layer.